One's girlfriend or wife. Usually used as a casual term of affection. Popularized by fans of the band Ween, as used on the EZ Board BBS dedicated to Ween. Such users generally attribute Buttsled as the father of the term.

"Last night the yak and I didn't do much, just drank some beer and listed to The Pod."

The word yak means blowjob and it can be used as any type of word such as using the noun version as a blowjob and also a verb as to give a blowjob. It can really be used as any word though because it is mysterious. This word began to be commonly known as blowjob in California when a famous celebrity Stephen Figura used it openly.

"Did she yak you last night?" -Maddie
"Yeah, she gave me the best yak ever" -Stephen
"wow that beer belly and Neapolitan ice cream is so yak" -Hannah